Function change_to_use_tmp_fields

sql/sql_select.cc:29975–30090

*/

static bool
change_to_use_tmp_fields(THD *thd, Ref_ptr_array ref_pointer_array,
			 List<Item> &res_selected_fields,
			 List<Item> &res_all_fields,
			 uint elements, List<Item> &all_fields)
{
  List_iterator_fast<Item> it(all_fields);
  Item *item_field,*item;
  DBUG_ENTER("change_to_use_tmp_fields");

  res_selected_fields.empty();
  res_all_fields.empty();

  uint border= all_fields.elements - elements;
  for (uint i= 0; (item= it++); i++)
  {
    Field *field;
    /*
      SUM_FUNC_ITEM will be replaced by the calculated value which is
      stored in the temporary table.
      The first part of the following test is for items that are expressions
      with SUM_FUNC_ITEMS, like 'sum(a)+1'. In this case we keep the original
      item, which contain an Item_ref that points to the SUM_FUNC_ITEM that
      will be replaced with a pointer to the calculated value.
      The second test is for window functions. Window functions contains
      only pointers to Item_refs, which will be adjusted to point to the
      temporary table.
    */
    enum Item::Type item_type= item->type();
    if ((item->with_sum_func() && item_type != Item::SUM_FUNC_ITEM) ||
       item->with_window_func())
      item_field= item;
    else if (item_type == Item::FIELD_ITEM ||
             item_type == Item::DEFAULT_VALUE_ITEM)
    {
      if (!(item_field= item->get_tmp_table_item(thd)))
        DBUG_RETURN(true);
    }
    else if (item_type == Item::FUNC_ITEM &&
             ((Item_func*)item)->functype() == Item_func::SUSERVAR_FUNC)
    {
      field= item->get_tmp_table_field();
      if (field != NULL)
      {
        /*
          Replace "@:=<expression>" with "@:=<tmp table
          column>". Otherwise, we would re-evaluate <expression>, and
          if expression were a subquery, this would access
          already-unlocked tables.
         */
        Item_func_set_user_var* suv=
          new (thd->mem_root) Item_func_set_user_var(thd, (Item_func_set_user_var*) item);
        Item_field *new_field= new (thd->mem_root) Item_field(thd, field);
        if (!suv || !new_field)
          DBUG_RETURN(true);                  // Fatal error
        new_field->set_refers_to_temp_table();
        List<Item> list;
        list.push_back(new_field, thd->mem_root);